This invention relates to a method and apparatus for recording channels of digitized information in data tracks on a record medium and, more particularly, to such a method and apparatus which is capable of recording such digitized information in a variety of different formats, while enabling common electronic circuitry to recover the recorded information regardless of the recording format which had been used.
Recently, digital recording techniques have been extended to various fields in which analog recording heretofore had been used. For example, high quality audio recording now can be achieved by using digital techniques. So-called PCM recorders have been proposed for recording audio signals in digital form on a suitable magnetic record medium, such as magnetic tape. U.S. Pat. Nos. 4,211,997 and 4,145,683 describe two of these digital audio recording techniques.
In analog audio recording, it is conventional to record the analog audio signals on magnetic tape which may be moved at a selected one of different speeds. It is known that, at higher recording speeds, the overall quality of the audio signal which may be recorded and reproduced is improved; but this improvement is achieved at a cost of relatively higher tape consumption. Thus, it is difficult to obtain long-playing record tapes of easily manageable size.
It is expected that similar considerations are applicable to digital audio recording. That is, digital signals of higher quality may be recorded and reproduced from magnetic media, such as magnetic tape, which are driven at faster speeds. Fortunately, the use of digital techniques provides relatively flexible capabilities of recording the digital signals in various different formats without loss of quality. For example, in one format, a number of channels of information are recorded in respective tracks on, for example, magnetic tape. Such multi-channel recording has long been used in professional analog recording applications, such as the preparation of master analog tapes from which phonograph records, prerecorded tapes, and the like, are produced. If each channel of information is recorded in a separate track, the maximum number of channels will be recorded but it is necessary to drive the tape at a relatively high speed. Thus, tape consumption also is relatively high. Tape speed and, thus, tape consumption, are reduced if each channel of digital signals is recorded in a plurality of tracks. For example, the tape speed may be reduced by one-half if each channel is recorded in two separate tracks, and the tape speed may be reduced by one-half again if each channel now is recorded in four tracks. Aforementioned U.S. Pat. No. 4,211,997 describes a digital audio recording technique wherein one channel is recorded in two separate tracks.
Generally, digital signals which are recorded in one of the aforementioned formats must be reproduced by apparatus which operates in accordance with that particular format. Typically, apparatus that is capable of operating in accordance with one format is not compatible with data that is recorded in a different format. That is, digital signals which are recorded on a magnetic tape in the format of one track per channel usually cannot be reproduced by apparatus designed for the format wherein digital signals are recorded in two (or four) tracks per channel. This lack of compatibility between different formats is a disadvantage of digital audio recorders of the type mentioned hereinabove.
As yet another example of different recording formats, it is typical to encode the digital signal (which may, for example, originate as a PCM signal formed of 16 bits) in one of various different types of error-correcting codes. One recent error correcting code which has been developed and which is particularly useful in recovering digitally encoded signals that may be subject to dropout, burst error, and the like, is the so-called cross-interleave error correction code described in, for example, U.S. application Ser. No. 218,256, filed Dec. 19, 1980. Other error-correction encoding techniques also are known, such as described in U.S. Ser. No. 195,625, filed Oct. 9, 1980. Typically, reproducing and decoding apparatus that is adapted to decode information that has been encoded in accordance with one encoding scheme, such as in accordance with one type of error-correction encoding scheme, generally is not compatible with digital information that has been encoded in a different encoding scheme.
Likewise, the encoded digitized information may be modulated prior to recording. Different types of modulations have been proposed, such as that described in U.S. Pat. No. 222,278, filed Jan. 2, 1981. Reproducing and demodulating apparatus that operates on data which which has been modulated in one format generally is not compatible to demodulate data which has been modulated in accordance with another format.
Accordingly, it is desirable to provide apparatus which is capable of recovering digitized information that has been recorded in various different types of formats. Also, depending upon the particular needs and objectives of the user, it is desirable to provide recording apparatus which is capable of recording digitized information in any one of such different formats.
In multi-channel digital recording/reproducing apparatus, it sometimes is desirable to edit the information in individual channels without affecting or disturbing the information in other channels. Also, the information that has been recorded in one track or in one channel may, at times, be re-recorded in another track or in another channel. Such operations generally are enhanced if information is provided to identify the different signals which are recorded in the different tracks or in different channels. If each channel or eack track is provided with suitable identifying signals, a significant amount of redundancy in the useful data tracks must be provided, thereby reducing the available space in which useful information can be recorded. Alternatively, if a separate control track is provided with identifying signals for each of the channels that are recorded on the record medium, then it is thought that such identifying signals must be selectively revised, or rewritten, whenever the information recorded in a corresponding track, or channel, is changed, such as by editing. However, the selective revision of, for example, only one of many identifying signals recorded in a control track is difficult and requires complex circuitry. Furthermore, such selective revisions to the identifying signals raise a strong possibility of producing an error during the signal-rewriting operation.
It is, therefore, desirable to provide a relatively simple technique for identifying the data recorded in each of the separate channels on the record medium.